Max Planck Institute for Solid State Research , Heisenbergstrasse 1 , D-70569 Stuttgart , Germany.
Institut de Physique , Ecole Polytechnique Fédérale de Lausanne , CH-1015 Lausanne , Switzerland.
Nano Lett. 2018 May 9;18(5):3203-3208. doi: 10.1021/acs.nanolett.8b00926. Epub 2018 Apr 12.
The small gap semiconductor α-RuCl has emerged as a promising candidate for quantum spin liquid materials. Thus far, Raman spectroscopy, neutron scattering, and magnetization measurements have provided valuable hints for collective spin behavior in α-RuCl bulk crystals. However, the goal of implementing α-RuCl into spintronic devices would strongly benefit from the possibility of electrically probing these phenomena. To address this, we first investigated nanoflakes of α-RuCl by Raman spectroscopy and observed similar behavior as in the case of the bulk material, including the signatures of possible fractionalized excitations. In complementary experiments, we investigated the electrical charge transport properties of individual α-RuCl nanoflakes in the temperature range between 120 and 290 K. The observed temperature-dependent electrical resistivity is consistent with variable range hopping behavior and exhibits a transition at about 180 K, close to the onset temperature observed in our Raman measurements. In conjunction with the established relation between structure and magnetism in the bulk, we interpret this transition to coincide with the emergence of fractionalized excitations due to the Kitaev interactions in the nanoflakes. Compared to the bulk samples, the transition temperature of the underlying structural change is larger in the nanoflakes. This difference is tentatively attributed to the dimensionality of the nanoflakes as well as the formation of stacking faults during mechanical exfoliation. The demonstrated devices open up novel perspectives toward manipulating the Kitaev-phase in α-RuCl via electrical means.
窄带半导体 α-RuCl 已成为量子自旋液体材料的有前途的候选材料。迄今为止，拉曼光谱、中子散射和磁化强度测量为 α-RuCl 体单晶中的集体自旋行为提供了有价值的线索。然而，将 α-RuCl 应用于自旋电子器件的目标将强烈受益于电探测这些现象的可能性。为此，我们首先通过拉曼光谱研究了 α-RuCl 的纳米薄片，并观察到与体材料相似的行为，包括可能的分数激发的特征。在补充实验中，我们在 120 到 290 K 的温度范围内研究了单个 α-RuCl 纳米薄片的电荷输运性质。观察到的温度相关电阻率与变程跳跃行为一致，并在约 180 K 处表现出转变，接近我们拉曼测量中观察到的起始温度。结合体相中结构和磁性之间的既定关系，我们将这种转变解释为由于纳米片中的 Kitaev 相互作用而出现分数激发。与体样品相比，纳米片中结构变化的转变温度更大。这种差异可以归因于纳米片的维度以及机械剥落过程中形成的堆垛层错。所展示的器件为通过电手段操纵 α-RuCl 中的 Kitaev 相开辟了新的视角。
